1. Field of the Invention:
This invention relates to di- and tripentaerythritol esters of isostearic acid characterized by having low volatility and excellent thermal and oxidative stability and which are useful high temperature lubricants. The products of this invention are especially useful as chain and bearing lubricants in applications where a wide range of temperatures are encountered.
2. Description of the Prior Art:
Esters based on polyols and aliphatic monocarboxylic acids are known and are widely used as automotive, industrial and turbine lubricants. These products are primarily derived from neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, or mixtures thereof, and saturated monocarboxylic acids having from about 5 to 10 carbon atoms. Many of these esters are derived from mixed acids of different chain length or branched and unbranched acids having the same or different chain lengths.
Polyol esters derived from higher fatty acids have recently been disclosed in U.S. Pat. No. 4,243,540 as a component for multi-grade lubricating oils useful in internal combustion engines. These esters are obtained by the reaction of a mixture of bifunctional and trifunctional polyols with a mixture of C.sub.6-8 linear monocarboxylic acids and C.sub.12-18 linear monocarboxylic acids. Also, in U.S. Pat. No. 4,053,491 branched-chain aliphatic ester products derived from branched-chain aliphatic polyols having from 2 to 6 hydroxyl groups and alpha-branched chain alkanoic acids having from 14 to 22 carbon atoms are disclosed as being useful for lubricants and hydraulic fluids. Polyol esters derived from mixed acids wherein iso-palmitic acid is a minor component are the subject of U.S. Pat. No. 4,234,497. The major acid component for these polyol esters is a C.sub.5-11 monocarboxylic acid or mixture and the polyol ester products are used as synthetic lubricant base stocks in automotive applications. Monocarboxylic acids containing up to 18 carbon atoms are disclosed in U.S. Pat. No. 2,975,152 for the preparation of esters of pentaerythritol or polypentaerythritols useful as plasticizers for vinyl halide polymers.
In U.S. Pat. No. 3,526,596 esters useful as lubricants for shaping and working metals at high temperatures are disclosed. The esters are derived from polyols having 2 to 12 hydroxyl groups and C.sub.12-22 fatty acids. Branched-chain acids obtained from oxidation of oxo process compounds or oxidation of alpha-olefins or alpha-olefin derived alcohols are indicated to be useful acids for the preparation of these polyol ester metalworking lubricants.
Isostearic acid esters of neopentyl glycol, trimethylol propane and pentaerythritol are disclosed by Boehringer et al. in U.S. Pat. No. 3,585,138 as useful base fluids for the preparation of synthetic greases. Also, in U.S. Pat. No. 3,074,981 isostearic acid esters of polyols containing a total of 5 to 7 carbon atoms and 2 to 4 methylol groups are disclosed as lubricants particularly adapted for use in jet engines.